JPH01262683A - Method for driving semiconductor laser - Google Patents

Abstract

PURPOSE:To display the high output low noise characteristics for accelerating the access time by a method wherein an exciting region is impressed with a gaining voltage while during low output and high output operations, an absorbing region is impressed with specified voltages alternately. CONSTITUTION:The oscillation threshold value voltage as injected evenly when an exciting region 12 and an absorbing region 11 are short-circuited is assumed to be V0. The exciting region 12 is impressed with DC bias V1(V1>V0) while the absorbing region is impressed with bias V2(V2>V0) during low output operation and bias V3(V3>V2) during high output operation. When the absorbing region 11 is impressed with the bias V2, this region 11 working as a saturable absorber, the low noise characteristics not exceeding the relative noise level of -120dB/Hz under optical output 1-3mW of returning light 1% can be displayed. On the other hand, when the absorbing region 11 is impressed with the voltage V3, the region 11 also becomes a gain region to bear the high output characteristics. Consequently, the high output low noise state can be brought about by simply changing the bias state in the absorbing region 11 while keeping the state of the exciting region 12 impressed with specified bias V1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser suitable for use as a light source for write-once type, rewritable type, etc. optical disks.

(Prior Art) A semiconductor laser with a low noise level is desired as a light source for write-once type, rewritable type, etc. optical disks in order to prevent errors during reading. 1 to 3 m for rewritable optical discs
At a low output level of W, a relative noise intensity (RIN) of -120 dB/Hz or less is required at 1% return light.

However, in optical disk devices, due to the structure of the pickup, the return light from the disk surface easily enters the semiconductor laser that is the light source.In general, index-guided semiconductor lasers with controlled transverse modes have high light interference. , this return light and the emitted light interfere, causing mode hop noise. As a result, the noise level of the light source increases, causing a system problem.

In order to reduce the feedback-induced noise of semiconductor lasers, a method of superimposing a high frequency from the outside has been proposed.IEICE Technical Research Report EO83-84P85
), in this method, a high frequency of 600 MHz or more is superimposed to reach the oscillation threshold, thereby imparting fluctuations to the injected carriers and making the longitudinal mode spectrum multimode. This multimode reduces the coherence of the light source, making it possible to maintain a low noise level even in the presence of returned light.

(Problems to be Solved by the Invention) However, in the conventional method, a high-frequency superimposition circuit is added externally, which hinders the reduction in weight of the optical head and makes it difficult to shorten the access time. Furthermore, the high frequency superimposing circuit increases the number of parts constituting the optical head, which also becomes a factor that hinders cost reduction. As described above, the conventional technology has problems to be solved in terms of access time and cost.

(Means for Solving the Problems) Means provided by the present invention to solve the above-mentioned problems are as follows:
An active layer and a second conductivity type semiconductor layer are sequentially formed as a Wi layer on a first conductivity type semiconductor substrate, and the second conductivity type semiconductor layer is electrically separated in the resonator axis direction to excite fi. A method for driving a transverse mode controlled semiconductor laser in which an electrically isolated structure is formed that divides the laser into two regions, a region and an absorption region, and the excitation region and absorption region are optically coupled.
During low output operation, a first voltage V3 large enough to generate a gain in the excitation region is applied to the excitation region, and a second voltage V2 is applied to the absorption region enough to cause a loss with respect to the oscillated light. is applied to the absorption region to cause automatic oscillation, and during high output operation, a first voltage Vl is applied to the excitation region and a first voltage Vl of sufficient magnitude to generate gain in the absorption region is applied. 3 voltage V, the absorption V4. It is characterized in that the high-output operation and the low-output operation are alternately switched.

(Function) In the driving method of the present invention, when a voltage is applied to the absorption region so as to cause a loss with respect to the oscillation light, the active layer in this region acts as a saturable absorber for the oscillation light. When a supersaturated absorber is introduced into a semiconductor laser medium, an automatic oscillation phenomenon occurs in which an intermittent oscillation state occurs. In automatic oscillation, oscillation is intermittently repeated at a high frequency corresponding to relaxation oscillation, so the injected carriers fluctuate and the longitudinal mode becomes multimode. This multi-mode longitudinal mode reduces coherence and provides low noise characteristics that are strong against returned light. Generally, it is difficult to obtain high output characteristics because the differential efficiency is low if the absorption region causes a loss to the oscillation light, but if a voltage is applied to the absorption region to create a high injection state, high Characteristics with stable transverse mode can be obtained up to the output. Low noise characteristics are required at low output levels during readout (
~3 mW), so by switching the bias level of the absorption region while applying a constant bias (1) that produces a gain to the excitation region, low noise and low noise during reproduction can be achieved.
According to the driving method of the present invention, a laser with high output and low noise characteristics that can be used as a light source for write-once and rewritable optical discs without using a high-frequency superimposition circuit can be obtained. You can get light.

(Example) A method for driving a semiconductor laser device, which is an example of the present invention, will be described below with reference to the drawings. 1 is a perspective view of a semiconductor laser device to which the embodiment is applied, FIG. 2 is a plan view of the semiconductor laser device of FIG. 1, and FIG. 3 is a perspective view of the semiconductor laser device of FIG. 1 to which the embodiment is applied. In Figure 0, which is a conceptual diagram showing the embodiment, 1 is an n-type GaAs substrate, and 2 is an n-type Aρ.

, 41G a O, S9A S cladding layer, 3 is n-type A
Ri o, s.

G a o, ssA 8 optical waveguide scrap, 4 is A I o,
osG ao, oxAs active layer, 5 is P type A, Q
o, s Gao, s As light reflective layer, 6 is P-type Aρo,
ssG a 0.62A S cladding layer, 7 is n-type G
1 is an aAs electrode layer, 8 is a P+ diffusion layer, 9 is an n-type electrode, 10 is a p-type electrode, 11 is an absorption region, 12 is an excitation region, and 13 is an electrode separation layer.

In manufacturing the semiconductor laser device shown in Figure 1, first the n-type G
A V-shaped Seifuku 5, 〇4, depth 2.0 parallel to <011> is formed on the aAs substrate 1 using an NH,OH-based etchant.
Form a μm groove. Thereafter, growth layers 2, 3, 4.5, and 6.7 are sequentially grown by a liquid phase growth method. Each layer has a flat part of 0.2 utr and 0.3 utr in order.
, 0.08um, 0.3 +u+, 1. Oull
l.

It is assumed to be 0.71 Jm. Since the spring is deep, n-type cladding layer 2
is not flat in the groove portion, and as shown in the figure, a thick structure of the optical waveguide NJ3 is formed in the light emitting portion, and a refractive index waveguide mechanism is formed in the horizontal direction. P+ in the light emitting area using 5ift as a mask
After forming the diffusion layer, a P-type electrode 10 and an N-type electrode 9 are formed. Furthermore, using a photolithographic technique and wet etching, electrode separation electrodes 13 with a width of 104 mm and an interval of 500 μm were formed except for a 30 μm area near the light emitting region.
30 in the vicinity of the 0-light emitting region formed until reaching the mold substrate 1
In the 1JI+ region, only the n-type GaAst pole layer 7 is removed.

The electrode portion M7R13 formed in this way allows the absorption region 11 and the excitation region i! to maintain the optical coupling between the absorption region 11 and the excitation region i! l1i12 can be electrically isolated. Finally, the excitation region 12 is 460 μm
The semiconductor laser device of FIG. 1 is formed by forming cleavage planes so that the absorption region 11 has a thickness of 30 μm. Note that the first
In the structure shown in the figure, the electrode separation is formed by etching.
However, a semiconductor laser device that operates similarly can be obtained even if electrode separation is performed using other methods such as proton injection.

Next, an embodiment of the semiconductor laser driving method of the present invention will be described with reference to the conceptual diagram of FIG. Let the oscillation threshold voltage be V when the excitation region 12 and absorption region 11 are short-circuited and uniform injection is performed. The excitation region 12 is provided with a DC bias V+ (
Vt>V. ), the absorption region 11 has a bias V2 (V2'>Vo) during low output operation, and a bias V2 during high output operation.
s (Vt>VO) is applied respectively. When the pi number V2 is applied to the absorption region 11, this region acts as a saturable absorber, so at an optical output of 1 to 3 mW and a return light of 1%, the relative noise intensity (RIN) is as low as -120 dB/Hz or less. Noise characteristics can be obtained.

On the other hand, when voltage V3 is applied to the absorption region 11, the absorption region 11
is also in the gain region, enabling high efficiency operation.

High output characteristics can be obtained. Therefore, high output and low noise operation is possible by simply changing the bias state of the absorption region 11 while applying a constant bias v1 to the excitation region 12.

Although the explanation has been given using a PCW construction using the LPE method using an n-type substrate as a laser structure to which the present invention is applied (1985 Spring IEICE National University, p. 920), it is also possible to apply the present invention to a semiconductor laser device. Alternatively, a p-type substrate may be used.

Further, the present invention can be similarly applied to other semiconductor laser devices in which the transverse mode is controlled, such as a self-line structure using the MOCVD method. Furthermore, not only the AUGaAs system but also the AJ
2GalnP.

The present invention can be implemented in the same manner with semiconductor laser devices made of other materials such as Ga1nAsP.

(Effects of the Invention) In the structure of the semiconductor laser device to which the present invention is applied, when a voltage is applied to the second conductivity type electrode of the absorption region so as to cause a loss with respect to the oscillation light, the active layer of the absorption region When a saturable absorber is introduced into a semiconductor laser medium that acts as a saturable absorber for oscillated light, an automatic oscillation phenomenon occurs in which an intermittent oscillation state occurs. Since automatic oscillation intermittently repeats oscillation at a high frequency corresponding to relaxation oscillation, the injected carriers fluctuate and the longitudinal mode becomes multimode. Due to this multi-modalization of the fiber modes, the coherence of the light source decreases, and 1~
Even at a low output of 3 mW, the relative noise intensity (
RI N ) -120 dB/Hz or less low noise characteristics can be obtained. It is difficult to obtain high output characteristics because the differential efficiency is generally low if the absorption region is left at a loss with respect to the oscillation light, but if a voltage is applied and carriers are injected to produce a gain in the absorption region, 30mW can be achieved. Characteristics with stable transverse mode can be obtained up to high outputs. Low noise characteristics are required at low output levels during readout (~3 mW
) Therefore, by applying a constant bias that produces gain to the excitation region 12 and changing the bias level of the absorption region, desired characteristics such as low noise during reproduction and high output during recording can be obtained. From the above, according to the method of the present invention, high output and low noise characteristics suitable for Et as a light source for write-once type, rewritable type optical disks, etc. can be realized without using a high frequency superimposition circuit.

Therefore, by employing the method of the present invention, it is possible to construct an optical disk system with short access time and low cost.

[Brief explanation of the drawing]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for driving a semiconductor laser device according to an embodiment of the present invention will be described below with reference to the drawings. 1 is a perspective view of a semiconductor laser device to which the embodiment is applied, FIG. 2 is a plan view of the semiconductor laser device of FIG. 1, and FIG. 3 is a perspective view of the semiconductor laser device of FIG. 1 to which the embodiment is applied. It is a conceptual diagram showing an aspect. 1--n-type GaAs substrate, 2--n-type Aρa, <+
GaO, 59AS cladding layer, 3-・-n type A')
o, s, Ga o, asAs optical waveguide layer, 4 ・A
ρo, oaG a O, 92A S active layer, 5...
p-type Aj! o, s Gao, s As light reflective layer, 6...
・p-type Aρ. ,. Gao, +□As cladding layer, 7...
・N-type GaAs electrode layer, 8...P+ diffusion layer, 9...
- N-type electrode, 10... P-type electrode, 11... Absorption region, 12... Excitation region - 13... Electrode separation groove.

Claims (1)

[Claims] An active layer and a second conductivity type semiconductor layer are sequentially stacked on a first conductivity type semiconductor substrate, and the second conductivity type semiconductor layer is electrically separated in the resonator axis direction to form an excitation region and an absorption region. In a method for driving a transverse mode controlled semiconductor laser, in which an electrically isolated structure is formed that divides the excitation region into two regions, and the excitation region and absorption region are optically coupled, during low output operation, the excitation region A first voltage V_1 of a magnitude sufficient to generate a gain is applied to the excitation region, and a second voltage V_1 of a magnitude sufficient to generate a gain in the absorption region is applied to the excitation region.
A voltage V_2 is applied to the absorption region to cause self-oscillation, and during high output operation, a first voltage V_1 is applied to the excitation region and the voltage is large enough to generate gain in the absorption region. 1. A method of driving a semiconductor laser, comprising: applying a third voltage V_3 of V_3 to the absorption region, and alternately switching between the high-output operation and the low-output operation.